Some problems with prestressed concrete sleepers durability

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 153
SOME PROBLEMS WITH PRESTRESSED CONCRETE SLEEPERS
DURABILITY
J. Pawluk1
, A. Cholewa2
, W. Kurdowski3
, W. Derkowski4
1
TrackTec, Warsaw, Poland
2
TrackTec, Warsaw, Poland
3
The Glass and Building Materials Division of the Institute of Ceramics and Building Materials, Cracow, Poland
4
Cracow University of Technology, Faculty of Civil Engineering, Cracow, Poland
Abstract
In the paper, the authors presented the hazards of concrete sleepers linked with delayed ettringite formation (DEF) as well as the
need to maintained of low alkalis content in cement. The authors also discussed the advantages of mechanical anchorage in
sleepers, applied in the BBRV technology. This method is based on the system of smooth bars anchorage, on the ends of the
strings with higher dimensions and is realized with the anchorage plates. It prevents of microcracks formation after tension
release.
Keywords: ASR reaction, DEF reaction, reinforcement rebars anchorage
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1. INTRODUCTION
From the eightieth the problems with concrete sleepers
deterioration have arose, which was caused by the change of
cement technology, from wet to dry method. Numerous
research [1- 6] have shown that in the majority of cases the
main reason of this deterioration was the delayed ettringite
formation (DEF). It was also establish in these studies what
are the causes of delayed ettringite formation [3, 6, 7]. It
seems then that it should end the story of the troubles with
concrete sleepers, but it does not the matter. In 2007 in
Germany, in the railway line from Berlin to Munich and
Hannover million sleepers must be changed, to replace the
damaged ones [8]. These sever events, principally from the
safety point of view, if the economic problems are even not
taken into account, deserve to remind of the rules which
assure the durability of concrete sleepers.
2. THE RULES ASSURING THE CONCRETE
SLEEPERS DURABILITY
2.1 External Destruction Mechanisms
The causes of external concrete sleepers destruction are
rather limited, because the sleepers in the railway lines are
positioned on subgrade composed of aggregate ballast. In
this conditions the aggressive solutions attack is rather
excluded and can take place very seldom. Thus the external
attacks are in the majority of cases limited to the frost
action. However, this action can be enhanced by the micro-
cracks formed in concrete, which can be caused either by
DEF, or by some errors of reinforcing steel bars release in
the case of prestressed concrete, which are the sleepers, or
by the lack of these reinforced bars anchorage. This problem
will be discussed in point 3.
The sleepers are produced from HPC of the strength in the
range from 80 to 90 MPa, and the content of high strength
cement CEM I 52,5 in concrete is high, as a rule over 300
kg/m3
. There are the reasons that neither frost attack [9] nor
carbonation [10] should not represent the serious causes of
concrete sleepers destruction.
2.2 Internal Destruction Mechanisms
The studies of Heinz and Ludwig [1] have shown that the
sleepers destruction was caused by DEF, however, the
causes of the instability of ettringite during heat treatment of
concrete were establish by Wieker et al. [3]. Wieker [3]
found that when the pore solution contains 400 mmol/l the
ettringite is unstable at 75o
C and is replaced mainly by
C4AH13 [Table 1]. Thus the sulphate ions remain in solution
[Fig. 1] and can react with aluminate ions during concrete
curing, after different period even two years, that gives
expansion.
Table 1: Sulphate phases in equilibrium with NaOH
solution as a function of its concentration and at different
temperature [3]
NaOH
concentria
-
tion
mmoles/l
Detected phases
25°C 75°C 100°C
0
400
700
1000
ett.*
ett.
ett.
ett.
ettringite
Ca(OH)2,
C4AH13
Ca(OH)2,
C4AH13
Ca(OH)2,
amorph. phases
ettringite
AFm, CaSO4,
Ca(OH)2
Ca(OH)2, CaSO4
C3AH6, Ca(OH)2,
CaSO4
* ett. – ettringit

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Fig. 1: Composition of the liquid phase in Portland cement
paste subjected to thermal treatment at 90o
C and then cured
in water at 20o
C, plotted as a function of time [3]
The time and the intensity of this expansion occurring is
depending on the heat treatment temperature [Fig. 2] [3].
The higher the temperature the higher the expansion and
shorter the time of its appearing. The expansion is enhanced
in the case of the high strength and rapid hardening cements
application. Unfortunately in the case of prestressed
concrete these type of cements are used.
Fig. 2: Expansion of mortars from Portland cement with
Na2Oe = 1.24, heat treated at different temperatures (time of
curing given on the plots), and subsequently matured at
humid atmosphere at temperature of 20o
C [3].
According to the studies of Wieker [3] and Glasser and
Damidot [11] the stability of ettringite during heat treatment
depends on the temperature and SO3 content in cement. At
the temperature of 70o
C and the concrete composition,
assumed in this paper, Pawluk [12] reported the stability of
ettringite at 500 mmol of NaOH in one litter of solution.
In further consideration we will assume that the concrete
composition was as follows: cement – 320 kg/m3
, SO3 in
cement 3%, w/c ratio 0.4, coarse aggregate – 1600 kg/m3
and sand 600 kg/m3
. According to these assumptions the
theoretical SO3 content in concrete will be about 0.4%. The
SO3 content in concrete can always be one of the method for
cement content verification.
The analyses of main type of aggregate used in sleepers
concrete, i.e. granite and basalt, have shown that the content
of soluble, thus reactive alkalis during heat treatment, is as a
rule very low, about 0.02% of Na2Oe. Thus it will give the
Na2Oe mass content in concrete of about 0.32 kg/m3
. In
ordinary cement, produced by dry method, the content of
total alkalis is about 1.0% of K2O and 0.25% of Na2O, and it
corresponds to about 0.91% of total Na2Oe and to about
0.8% of soluble Na2Oe. In concrete it will give 2.56 kg/m3
.
Taking into account the soluble Na2Oe in aggregate equal
0.02%, their income to concrete can be calculated as 1600 x
0.0002 = 0.32 kg/m3
. The total content of soluble Na2O in
concrete will be 2.98 + 0.32 = 3.30 kg/m3
. 3.30 kg is equal
to 2448.4 g of Na, which can form 4258 g of NaOH in
concrete. It will correspond to 33.27 g of NaOH/l of
solution, thus 0.832 mmol/l of solution. It is much higher
than the permissible content establish as 500 mmol/l [12].
For the heat treated concrete as in the sleepers production it
was necessary to apply low alkali cement and in Poland the
content of total Na2Oe in this cement is lower than 0.6% and
lower than 0,5% of soluble Na2Oe. The soluble alkalis
content in concrete will be: 0.005 x 320 = 1.60 kg/m3
+ 0.32
of Na2O from aggregate which gives the total content of
1.92 kg/m3
. It means 1.92 x 0.742[Na/Na2O] = 1.425 kg of
Na. It corresponds to 2.48 kg of NaOH and 19.38 g/l of
solution and 485 mmol/l. It is lower then found by Pawluk
[12] threshold value. If we take, as a limit for total alkali
content in cement 0.8% [soluble 0,7%], calculation shows
that it will correspond to 2.24 kg of Na2O kg/m3
and + 0.32
Na2O from aggregate = 2.56 kg/m3
. It gives 1.90 kg of Na
which corresponds to 3.3 kg of NaOH and 25.8 g/l of
solution and 645 mmol/l, which is much higher than the
threshold value [12]. It was the cause that in concrete with
cement containing 0.78% of soluble alkalis ettringite was
not stable at heat treatment at 70o
C.
It should be also underlined that the low alkalis content in
cement is also an efficient method for hindering of the alkali
silica reaction in the case of reactive aggregate usage in
concrete production [13].
3. PROBLEM OF SLEEPERS
REINFORCEMENT
In typical prestressed concrete elements the tensioning force
is transmitted on concrete through the adhesion of the
strings and cover of hardened concrete. The constrains of
adhesion are usually defined as the tangential stress,
uniformly distributed on the string surface. At this surface
the mechanism of adhesion are the following: chemical
adhesion, friction on the contact of steel bar with concrete
and mechanical meshing. The chemical adhesion is causing
the compressive strength on the bond of steel bar with
concrete, however, it can be broken, even at very low slip of
the string in concrete cover. In Fig. 3 the adhesion stress in
non-cracked concrete is presented in the initial section of the
diagram, ranging to point A [14].
The chemical adhesion can be also broken by the
microcracks formation in concrete, in the neighbourhood of
string. It is assumed that the tensioning force of steel bars in
concrete is in the range from 0. 5 to 1.0 MPa.

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The friction of steel bar with concrete is very important in
transmitting forces between this bar and concrete and
depends in high degree of the string shape. It even can
represent of 35% of final tensioning strength of concrete.
The mechanical meshing, formed on the bars surface
roughness, has a decisive influence on concrete tensioning
to the reinforcement. It depend significantly on the string
surface and nowadays the bars with deformed surface, or
multi-weaves wires, are commonly used in prestressed
elements. When the maximum bond strength is reaching the
microcracks in concrete wedge are beginning to form, in the
strings pockets and the slip is appearing. It can be caused
also, in minor degree, by shrinkage or other concrete volume
changes.
Fig. 3: Typical relations of tensioning stress from slip [15].
In classic prestressed concrete elements the total tensioning
force on concrete is transmitted in section of length lpt ,
called the transmission length. Out of this section the
compressive stresses of tensioning are successively
propagating on whole element intersection. The linear
distribution of this stresses propagation appear only in the
intersection at the distance from the element front equal ldisp .
These both section are shown on Fig. 4.
lpt
ldisp
x
d
h
Fig. 4: The transmission and propagation sections length in
prestressed concrete element
The length of these sections depend significantly on
concrete mechanical properties, chiefly of the tension
strength, but also on hardness, and on tensioning force and
string diameter.
In the case of such specific construction as prestressed
concrete mono-block sleepers the transmission length is a
main designing parameter, because the very high effort of
the under-rail zone, is relatively close located to the sleeper
front.
The transmission of tensioning force to the sleeper front
zone, in which the strings are anchored by tensioning only,
causes the composed, spacial stresses state, composed of the
longitudinal stress streams, compressing concrete (parallel
to the sleeper axis) and the lateral tensile stresses. The
recently published Model Code 2010 [16] is defining three
types of cracks formation in the sleeper front of prestressed
concrete, which can have basic effect on correct strings
anchorage in concrete:
 bursting effect – designed as „1” in Fig. 5, caused
by lateral tensile stresses in concrete,
 spalling effect – designed as „2” on Fig. 5, in the
end zones of concrete elements, particularly with
thin-walls ones,
 splitting effect – designed as „3” , near the contact
surface with the string, caused mostly by to close
placed the neighboring strings.
Fig. 5: The stress streams directions and possible damage of
near-front zone of prestressed concrete element [16].
Splitting phenomenon can be easily prevented by confined
concrete with suitably shaped bars, for example in the form
of stirrup. According to the MC [16] recommendations to
prevent the cracks formation in the contact zone with the
string the minimum spacing between strings assuring, not
lower than (2÷3) Øs (where Øs is the nominal string
diameter) and minimum string cover, not lower than (2,5÷4)
Øs.
Frequently the aforementioned phenomena are
superimposing and their total effect can lead to the total loss
of load capacity, of whole element.
It will be interesting to describe the prestressed concrete
sleepers with strings in the form of weaves, composed of
three smooth wires with the diameter of three mm (weave
Øs ≈ 6,5 mm). The weaves were situated in two groups
placed vertically, one above the second. These sleepers were
frequently damaged.
The front of this sleeper is such configurated, that the ends
of particular tensioning string groups were placed in the
concrete tongue, of relatively low width. In the near-front
zones the concrete confining was not applied.

_______________________________________________________________________________________
Fig. 6: The damaged sleeper front; [source the authors
archive].
The defects, in the form of concrete cracking and significant
spalling, are caused by incorrect designing of the sleepers
near-front zone. In these damage probably all the defects
defined in the MC [16] instruction take place. The
cumulating of the relatively high tensioning force, due to
several weaves placed at low distance, caused the
microcracks due to the significant transverse deformation of
highly compressed concrete i.e. spalling effect and bursting
effect. This effect should occurs in the place in which
several strings were placed, with low spacing. Applying in
the sleepers ends the tongues with low transverse
intersection of concrete without circumferential
reinforcement, caused spalling effect. However, the
phenomenon of unsymmetrical damage of sleeper is
probably due to the non-uniform tension release, during
sleepers production.
The majority of described damage of near-front zone of the
sleepers were formed probably at tensioning release of
concrete, but their intensity were significantly lower. Only
the cyclic, dynamic loading caused by railway exploitation
and frost action, caused the significant development of these
damage.
The attention should be also paid to the lack of corrosion
protection of tensioning weaves ends in the case of
reinforcing strings anchorage only through adhesion.
The alternative solution to the aforementioned anchorage of
tensioning strings in sleepers is the method with mechanical
anchorage, applied in the BBRV technology, which is used
in several European countries, also in Poland. The system of
smooth bars (diameter of 7 to 8 mm) anchorage, on the ends
of the strings with higher dimensions, is realized with the
anchorage plates. Tensioning is solved through the
tensioning screws in the anchor aging plates, placed at some
distance from the element front. This solution is shown in
the Fig. 7 and its position in the mould, before concrete
placing, in Fig. 8.
Fig. 7: Anchorage plate
Fig. 8: The damaged sleeper front. Source the authors
archive.
4. FINAL REMARKS
In to prevent the prestressed concrete sleepers from damage
and assure their durability some fundamental rules must be
observed. There are the following:
 assure the usage of low alkali cement,
 the temperature of heat treatment must not exceeds
70o
C, inside the concrete elements,
 the application of BBRV technology should be
seriously taken into account.
The studies of four different systems of strings anchorage,
carried out in 2013 in Technical University in Kraków, have
shown that the BBRV technology is assuring the highest
load ability of sleepers by 23 to 36%.
REFERENCES
[1]. Heinz D., Ludwig U., 8th ICCC Rio de Janeiro, vol. V,
p. 189, Rio de Janeiro 1986.
[2]. Heinz D., Ludwig U., Rudger L., Concrete Pecasting
Plant and Technology, 11, 56 (1989).
[3]. Wieker W., Herr R., Schubert H., Proc. Int. Coll.
Corrosion of Cement Paste, Mogilany 16–17 November (ed.
W. Kurdowski), p. 3, Kraków 1994.
[4]. Kelham S., Cem. Contr. Composites, 18, 171 (1996).
[5]. Kelham S. 10th ICCC Göteborg, vol. IV, paper 4IV059,
Göteborg 1997.
[6]. Wieker W., Scrivener K. L., 9th ICCC New Delhi, vol.
I, p. 449, New Delhi 1992.
[7]. Glasser F. P., Damidot D., Atkins M., Adv. Cem. Res.,
26, 57 (1995).
[8]. Schmitt J., Pfusch am Gleis, Der Spiegel 10/2008.

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[9]. Pigeon M. and Pleau R., Durability of concrete in cold
climates, Taylor & Francis, London 1995.
[10]. Nagataki S., Ohga H., Kyum Kim E., Proc. 2nd Int.
Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolanas
in Concrete (ed. V. M. Malhotra), ACI SP–91, p. 521,
Madrid 1986.
[11]. Glasser F. P., Damidot D., Atkins M., Adv. Cem. Res.,
26, 57 (1995).
[12]. Pawluk, submitted for publication in Cement Wapno
Beton.
[13]. Oberholster R. E., Wan Aardt J. H. P., Brandt M. P., w
„Structure and Performance of Cements” (ed. P. Barnes), p.
365, Appl. Science Publ., London 1983.
[14]. Hosseini, S. J. A.; Koushfar, K; Rahman, A.B; Razavi,
M., “The bond behaviour in reinforced concrete, state of the
art”, Cement, Wapno, Beton, 2, 2014.
[15]. Sungnam Hong Sun-Kyu Park, Uniaxial Bond Stress-
Slip Relationship, Advances in Materials Science and
Engineering, Aericle ID 328570, 12 pages [2012].
[16]. „Model Code 2010 - Final draft”, fib Bulletin 65 and
66, Swiss Federal Institute of Technology Lausanne,
Switzerland, 2012.
BIOGRAPHIES
J. Pawluk – the graduate of Fachhochschule Niederrhein,
Germany, Faculty of Chemistry, Chemical Technology,
President and Chief Executive Officer, Track Tec S.A.
A. Cholewa – the graduate of Silesian University of
Technology, Faculty of Automatic Control, Electronics and
Computer Science, Ph. D. - Warsaw School of Economics,
Member of the Board, Chief Technical Officer, Track Tec.
S.A.
W. Kurdowski – professor at The Glass and Building
Materials Division of the Institute of Ceramics and Building
Materials in Cracow. Expert in cement chemistry.
W. Derkowski – Ph. D., lecturer in Building engineering
branch, Faculty of Civil Engineering, Cracow University of
Technology.

Some problems with prestressed concrete sleepers durability

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